The present invention relates to a hydrogel based on a low-molecular weight compound, particularly to a supramolecular hydrogel subjected to a reversible gel-sol phase transformation.
Conventional soft materials represented by hydrogels are mainly composed of synthetic polymers or biopolymers such as polysaccharides. However, in order to control the structures and properties such as substance-holding capacity and permeability of the hydrogels on a molecular (nano) level, the nano-structures and surface chemical structures of the gels should be accurately controlled, and this poses a technical limitation on the conventional polymer-based hydrogels. These issues hold a key to impart new functions such as high-speed stimulus response and chemical-mechanical energy conversion, etc. to the hydrogels.
On the other hand, if a new method were devised to form hydrogels of nano-level supramolecular assemblies by self-assembling low-molecular weight compounds, it would be possible to accurately control their nano-structures and properties through the chemical structure of constituent molecules and the characteristics of supramolecular assemblies (phase transformation phenomenon, etc.).
The development of a supramolecular hydrogel using a low-molecular weight compound needs the development of an artificial supramolecular assembly that spontaneously forms a hydrogel. Though there are a lot of known examples of organogelators that can be self-organized in an organic solvent to form a gel, supramolecular assemblies capable of forming a gel in an aqueous solution in a self-organizing manner are not known at present with respect to their general molecular design.
Accordingly, an object of the present invention is to provide a supramolecular hydrogel based on a compound having a relatively low molecular weight, which is synthesized according to the molecular design of synthetic bilayer membranes.
As a result of intense research in view of the above object, the inventors have found that a supramolecular hydrogel can be obtained from a low-molecular weight compound, by adding an anion having a molecular weight of 90 or more to an aqueous dispersion of a cationic amphiphile comprising a linear or branched alkyl group having 10 or less carbon atoms in a hydrophobic moiety. The present invention is based on this finding.
Thus, the hydrogel of the present invention comprises a combination of a cationic amphiphile comprising a linear or branched alkyl group having 10 or less carbon atoms in its hydrophobic moiety and an anion having a molecular weight of 90 or more.
The cationic amphiphile used in the present invention comprises a hydrocarbon moiety that is a low-molecular weight compound having 10 or less carbon atoms, differing from the conventional molecules forming bilayer membranes that comprise highly crystalline, long-chain alkyl groups, etc., in their hydrophobic moieties. Because the cationic amphiphile used in the present invention has lower molecular orientation than the general molecules forming bilayer membranes, it cannot form a hydrogel without combination with other compounds. However, it can form a stable hydrogel when combined with anions having a molecular weight of 90 or more.